Three Forks sits at the intersection of three blue-ribbon trout rivers, each with a distinct character. The Madison — cold, fast, and intensely productive — runs south toward Ennis and is one of the most celebrated dry-fly rivers in Montana, known for its prolific hatches and large brown and rainbow trout. The Gallatin cuts through a dramatic canyon south of Bozeman, with swift runs and smaller fish. The Jefferson, broader and slower, offers good streamer fishing and some trophy browns in its deeper pools.
All three rivers are accessible to wade fishermen from public land and state access sites, and none requires the helicopter or ranch access that prices serious fly fishing out of reach on some Montana rivers. The Missouri River itself, immediately downstream of the confluence, is also well regarded and fished heavily by float anglers.
Local guide services operate out of Three Forks and Bozeman. If you only have one day, the Madison is the default choice. The spring and fall shoulder seasons are generally less crowded than July and August, and the fishing can be better — the Madison in particular can become frustratingly clear and low in late summer.